Hydrological and Environmental Dynamics in Las Güixas Show Cave: Tourist Exploitation and Flood Risk Management

Show caves are great natural attractions and constitute important economic engines for particular rural areas. However, cave management requires knowledge of the cave dynamics to ensure adequate exploitation and conservation (e.g. number of visitors, amount of CO2, other impacts). Show caves located close to the hydrological base level can be affected by a sudden rise of the water level in response to rainfall events, exposing touristic facilities, visitors and staff to flood risk. Here we present a monitoring campaign in Las Güixas show cave, a small tourist cave located in the Central Pyrenees, to guide in developing an adequate flood risk management plan (FRMP). Cave monitoring includes temperature, relative humidity, CO2 concentration and water level measurements to characterize the different cave sections, as well as to assess the possible influence of the visitors on the cave dynamics. The tourist section is very well ventilated due to intense air flow associated with a chimney effect, and therefore CO2 remains low and temperature shows high thermal oscillations throughout the year. During the maximum number of visits per day, the CO2 generated by the tourists increases, however, is quickly reduced by the ventilation. Water level monitoring shows clear rises depending on the amount of rainfall and snowmelt in the catchment area. However, the water level does not always respond to given rainfall amounts in the same way, indicating that the water retained in the karst system plays an important role. Water can flood the tourist section forcing to cancel the following visits which generates economic losses. In addition, the higher water flow increases the natural inputs of CO2 in the cave atmosphere due to degassing. Las Güixas cave monitoring shows that anthropogenic CO2 emissions remain substantially lower than CO2 concentrations during the flood events.